I see you are 310 but if you can make it up to Valencia, Big John's is the place to go. I also have 01 Xterra 4WD V6 with 216,050 miles on it and I take my X there for any work I need done. Very reliable and very fair on the prices.
nice 216k .....my pathy had 293K my 280 had 486k.
another thing to try which is quick and cheap is the seafoam treatment. You take off one of the vaccumn lines and let it suck in some sea foam. It clean the throttle body and some other vital parts. It will smoke like a crack house but it does work. Pour the rest in the tank. I dont remeber exactly which one so go to the new X forum and read the post.
Or It can be as simple as bad gas.
The reconmended interval for gen 1 is 110K so I doubt it is this.